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"It looks good now. But if you lock in 4.69 per cent for three years that could be logically more advantageous."

She said most people who locked in a low rate spent the savings rather than putting them aside to pay off more debt or house maintenance.

"Do the budget now to see what will be viable in 18 months time."

David Tripe, a banking expert at Massey University said the rate suggested HSBC were being a "bit less greedy with their margins" than the other banks.

Tripe said HSBC's assets had been shrinking and the timing of the offer probably had something to do with the bank trying to meet targets or replace loan business that was being rolled over.

He also doubted other banks would match the offer but he said those with mortgage debt of over $500k should still be able to negotiate a good rate with their bank.

The rate is just shy of the record low rate of 3.95 per cent which HSBC ran with this time last year.

It is only available for owner-occupiers who borrow more than $500,000 or have $100,000 in savings and investments with the bank.

Existing HSBC premier customers can also get it if they borrow an extra $100,000.

An HSBC spokesman said the rate was not a loss leader.

"This is a very competitive rate, but it is also profitable for us and is not a loss leader."

He said like other banks HSBC got its funding from a mix of deposits, wholesale funding and group support but unlike other banks it was less reliant on wholesale funding.

"We are keen to grow our mortgage business here in our target mass affluent market segment, and the HSBC Group continues to be supportive of our business in New Zealand."

Glen Tonks, head of retail banking and wealth management at HSBC in New Zealand, said the rate was being offered for a limited time.

"With market uncertainty having increased in recent times, we are pleased to be able to provide our owner occupier customers with certainty over the short-to-medium term with this 3.99 per cent per annum 18 month-fixed mortgage offer."

HSBC's 3.99 per cent rate special follows a flurry of mortgage rate increases since the start of the year with a number of banks increasing longer term fixed rates more than once.

Some banks have also increased their floating rate - an unusual move in what has been a falling cash rate environment.

Last week the Reserve Bank decided to keep the official cash rate on hold at 1.75 per cent - but rate watcher Canstar warned home loan rates will continue to rise this year.

"Canstar expects home loans rates to continue to rise in 2017 as banks and other lenders aim to pass on the pressures of overseas funding costs, while looking to retain margin," Jose George, Canstar New Zealand general manager said in a statement in the wake the Reserve Bank decision.

"For existing home loan customers Canstar recommends that they review their budgets and stress test their repayment capability through online calculators to ensure that they can accommodate any potential increased cost of servicing their loans."